1. Field of the Invention
This invention relates to a half-speed mirror moving mechanism and a lens moving mechanism which allows continuous variation of magnification in a variable magnification-type copying machine in which the magnification can be varied from an enlarging magnification to a contracting magnification and vice versa.
2. Description of the Prior Art
Some of the conventional, variable magnification-type copying machines employ a zoom lens system such as that disclosed by Japanese Patent Application Nos. 145988/1980 and 37841/1980 which have been filed by the present Applicant. The zoom lens system needs two lens groups which are operated independently. Accordingly, a copying machine using the zoom lens system is disadvantageous because it requires a large number of lenses and is intricate in design.
Japanese Patent Application Laid-Open Nos. 77762/1980 and 77763/1980 disclose a variable magnification-type copying machine which is capable of several magnifications in which, as shown in FIG. 1, the scanning starting position of a half-speed mirror M12 and the position of a lens L10 are changed for each change in magnification. In the copying machine which has a full-speed mirror M11 and the half-speed mirror M12 arranged as shown in FIG. 1, as the half-speed mirror M12 is moved from the point T to the point T', an original illuminating point is shifted from the position t to the position t'. The movement of the illuminating point must be corrected for each magnification. Furthermore, the optical axis on the full-speed mirror M11 is shifted and, therefore, the full-speed mirror must be large. If it is desired to provide an enlarging magnification larger than one (a magnification of one representing a life-size magnification), the lens L10 must be moved towards the half-speed mirror M12. In this case, the lens may be brought into contact with the half-speed mirror, or the lens may block the optical half of the half-speed mirror, thus making it impossible to provide a sufficiently large enlarging magnification in practice. Furthermore, since the scanning starting position of the half-speed mirror M12 and the position of the lens L10 are limited, it is impossible to continuously vary the magnification. In addition, the prior art copying machine is intricate in construction.